Tucson, Arizona (CNN) -- Criminal defendants are expected to make initial appearances in federal courts in Phoenix and Tucson on Friday in connection with what one federal agency calls the largest human smuggling investigation in its history.

U.S. and Mexican authorities arrested dozens of people Thursday in what U.S. officials say is "the culmination of a comprehensive year-long" investigation focusing on shuttle buses operating along the border between Arizona and Mexico.

"This operation has dealt a serious blow to the infrastructure of some of Arizona's most prolific and profitable human smuggling organizations -- organizations that made their money by moving people," John Morton, homeland security assistant secretary for Immigration and Customs Enforcement, said at a news conference Thursday afternoon.

The investigation is called Operation In Plain Sight because of what officials call the "brazen nature" of the shuttle services, allegedly part of a confederation of illegal immigrant smuggling rings.

The investigation "included unprecedented cooperation with Mexico's Secretariade Securidad Publica," and it "ultimately implicated high-level members of human smuggling organizations" in northern Mexico and the Arizona cities of Phoenix, Tucson and Nogales, ICE said.

Eight hundred agents and officers from nine federal and local law enforcement agencies fanned out across Arizona on Thursday, making arrests in the three above cities, plus Rio Rico, and shutting down businesses. Authorities in Mexico and Tennessee also made arrests.

ICE, which is part of the Department of Homeland Security, said owners and employees of five Arizona commercial shuttle services are among the 47 criminal suspects taken into custody after search and arrest warrants were executed in Arizona.

Mexican agents made four criminal arrests, according to Virginia Kice, ICE's Western regional communications director. Authorities announced two arrests in Tennessee, a location underscoring the national reach of the smuggling operation.

Here's how the rings operated, federal authorities said: Smugglers would help illegal immigrants enter the United States near a border city such as Nogales. They would then be transported to Tucson, where one of the shuttle vans would take them to Phoenix.

Once there, they would rendezvous with another vehicle and be taken to a drop house, and they would then be moved to cities all over the United States, authorities said.

Illegal immigrants were allegedly issued phony tickets for shuttle trips, which enabled drivers to claim they were operating legitimate businesses if they were stopped by law enforcement.

While most of the smuggled people identified in the investigation came from Mexico and Central America, others came from far-flung locations, such as China.

"The defendants wrongly believed they could operate with impunity by hiding behind the veil of legitimacy these businesses provided. Using our investigative expertise, we've dismantled these transnational organizations and literally seized the engines that were driving the criminal enterprise," Morton said.

The timing of the raids has drawn criticism from immigration rights groups.

"I think we're getting absolutely mixed messages," Jennifer Allen, director of Border Action, said Thursday. "I saw that just yesterday, first lady Michelle Obama said she wants to see immigration reform happen, and then we wake up this morning and we have ICE raids intensively throughout the state of Arizona."

The first lady visited Mexico this week, where she met with her counterpart, Margarita Zavala de Calderon.

ICE officials say politics played no role in the operation. They say the massive investigation and resulting sweep represent a shift in enforcement strategy.

For years, law enforcement officials concentrated on busting illegal immigrant drop houses. Now, federal officials say, they are after the transportation networks that supply the smugglers' human cargo.